Epidemiological studies provide strong evidence that diet can modify cancer incidence. Populations concuming legume-derived products exhibit significantly decreased rates of breast, colon and prostate cancer. Legume products contain an array of anticarcinogens of diversified structures. Biochemical evidence correlating their presence due to legume consumption and cancer reduction in human populations is lacking. Our long term objective is io understand the quantitative relationship between soybean consumption and cancer reduction. In this proposal, we will investigate the pharmacokinetics of soybean-derived anticarcinogens in humans. The hypothesis to be tested is that continuous consumption of soybean products is necessary to maintain constant blood and tissue levels of isoflavones. This will be tested as follows: 1. The influence of food processing on isoflavone levels will be determined in different commercial soybean products. 2. The influences of age, sex, dietary habit, and disease state on absorption, disposition, and clearance of isoflavones will be determined prior to and/or after a shot term and chronic soymilk diets. The levels of isoflavones while on an unrestricted diet, at 1 week off a soybean-derived diet, at 1-4 weeks on a soybean diet and at 1-2 weeks after withdrawal from a 4 week-soybean diet will be analyzed. These will be measured in blood, urine as well as tumorous and non-tumorous breast and colon tissues. The levels of isoflavones will be compared before and after soymilk consumption, between different age or sex groups, between Asians and non-Asians, among cancer subjects, normal vegetarians, and normal omnivores, or between tumor and non-tumorous tissues. The Greater Houston-Galveston area has a large Asian population (Chinese, Vietnamese, and Indians) accustomed to a high soybean content diet. Many individuals in this population are also vegetarians. Furthermore, large Hispanic and Black populations are also available in this area. Thus, the population composition is uniqudly suited for current pilot and future large scale dietary intervention trials. This study will provide a rational basis for future dietary studies of cancer prevention by soybean meals.